Micro-electromechanical systems (MEMS) technology has achieved wide popularity in recent years, as it provides a way to make very small mechanical structures using conventional batch semiconductor processing techniques. One such device is the MEMS variable capacitor, or varactor.
It is desirable for a varactor to have a wide usable range of capacitance values. Unfortunately, the tunable range of a MEMS varactor is severely limited by its initial air gap dimension. For a typical analog varactor, due to electro-static pull-in phenomena, the typical tunable range is about 33% of its initial (un-driven) state. In a binary varactor, the tuning ratio (Con/Coff) is typically between 5:1 to 30:1, depending upon its initial gap and actuation voltage.
This limitation is sometimes addressed by increasing the initial air gap distance between capacitive plates. The larger the initial air gap, the higher the tuning ratio. At the same time, however, larger initial air gaps give rise to increase actuation voltage.
Furthermore, in such prior art systems, the MEMS varactor is fabricated first, then sealed in an enclosing package. This increases processing steps and results in a device that is relatively large and complex.
Accordingly, it is desirable to provide compact MEMS varactor structures that have a wide tunable range and/or tuning ratio. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.